1. Field of Invention
The present invention is directed to an apparatus and method for providing multimedia conferencing services with an unspecified bit rate (UBR) quality of service class over an asynchronous transfer mode (ATM) network.
2. Description of Related Art
Multimedia conferencing over an ATM network is generally provided with either a constant bit rate (CBR) quality of service class or a variable bit rate (VBR) quality of service class. The CBR class guarantees that the multimedia conferencing service will be provided at a peak cell rate (PCR), and the VBR class guarantees at least a minimum cell rate (MCR) for the multimedia conference. A cell is a packet of 53 bytes (i.e., 424 bits). Thus, a cell rate of 10 cells per second corresponds to a bit rate of 4240 bits per second. Because the CBR and VBR quality of service classes guarantee particular cell rates, the transmission of signals for those service classes are given priority over other ATM network communications. Therefore, the CBR and VBR quality of service classes guarantee a particular service quality, and thus, are relatively costly classes of service. Thus, new technology is needed to provide economical multimedia conferencing services over an ATM network with a satisfactory quality of service.
The invention provides an apparatus and method that provides economical multimedia conferencing services to multiple parties over an ATM network. Service satisfying different performance criteria may be provided to each party based on networking conditions beyond the control of the parties (e.g., availability of bandwidth, switches, circuits, buffers, and the like) or based on the preferences of the respective parties, as described in U.S. patent application Ser. No. 09/371,864, filed Aug. 11, 1999, which is incorporated herein by reference in its entirety.
Using the invention, multimedia conferencing services are provided at a UBR quality of service class. The UBR class does not guarantee any specific bandwidth over the ATM network nor does it provide any congestion control mechanisms. Further, in the event of network congestion, a service provider will start dropping cells from the UBR class multimedia conferences before dropping cells from CBR and VBR conferences. Therefore, the UBR class of service is very vulnerable to network congestion.
However, the UBR class of service is inexpensive to provide because there is no guaranteed cell rate. Thus, the UBR class of service is desirable as long as output quality can generally be maintained at or above a satisfactory level. It is an object of the present to provide a UBR class of service that maintains a satisfactory output quality. Accordingly, once a UBR class multimedia conference is commenced, a multimedia bridge equipped with ATM network interfaces monitors the ATM network for congestion. If the multimedia bridge detects congestion along the ATM network paths used for sending and receiving the multimedia conference signals, the multimedia bridge either redirects the signals along another ATM network path capable of handling the signals or scales down the signals for transmission.